Package-on-Package Structure Including a Thermal Isolation Material

ABSTRACT

A semiconductor device includes a first package component and a second package component. The first package component has a first die formed on a first substrate. A second package component has a second die formed on a second substrate. A thermal isolation material is attached on the first die, wherein the thermal isolation material thermally insulates the second die from the first die, and the thermal isolation material has a thermal conductivity of from about 0.024 W/mK to about 0.2 W/mK. A first set of conductive elements couples the first package component to the second package component.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.16/580,617, entitled “Package-on-Package Structure Including a ThermalIsolation Material,” filed on Sep. 24, 2019, which is a continuation ofU.S. patent application Ser. No. 15/228,098, entitled,“Package-on-Package Structure Including a Thermal Isolation Material andMethod of Forming the Same,” filed on Aug. 4, 2016, now U.S. Pat. No.10,490,539 issued Nov. 26, 2019, which is a continuation of U.S. patentapplication Ser. No. 13/671,665, entitled “Package-on-Package StructureIncluding a Thermal Isolation Material and Method of Forming the Same,”filed on Nov. 8, 2012, now U.S. Pat. No. 9,418,971 issued Aug. 16, 2016,which applications are incorporated herein by reference.

BACKGROUND

Package-on-package (POP) is becoming an increasingly popular integratedcircuit packaging technique because it allows for higher densityelectronics.

A conventional package-on-package structure may include a bottom packagecomponent and a top package component. The bottom package component mayinclude a bottom die attached to a bottom substrate and the top packagecomponent may include a top die attached to a top substrate. The bottompackage component is coupled to the top package component typically by aset of conductive elements, such as solder balls. In operation, bothpackage components generate heat. However, excessive heat that isgenerated by the bottom die, especially where the bottom die is a devicedie, may cause damage to the top die. The heat can also cause thermalstress and warpage in the package-on-package structure leading to cracksin the solder balls. Even with the use of molding compounds in thepackage-on-package structure, the problem of excess heat and warpagestill cannot be entirely eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure are best understood from thefollowing detailed description when read with the accompanying figures.It is emphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a flowchart of a method of fabricating a package-on-packagestructure according to various embodiments of the present disclosure.

FIGS. 2-6 are cross-sectional views of a top package and/or a bottompackage at various intermediate stages in the manufacture of apackage-on-package structure, in accordance with various embodiments ofthe present disclosure.

DETAILED DESCRIPTION

In the following description, specific details are set forth to providea thorough understanding of embodiments of the present disclosure.However, one having an ordinary skill in the art will recognize thatembodiments of the disclosure can be practiced without these specificdetails. In some instances, well-known structures and processes are notdescribed in detail to avoid unnecessarily obscuring embodiments of thepresent disclosure.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present disclosure. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments. It should be appreciated that the followingfigures are not drawn to scale; rather, these figures are intended forillustration.

FIG. 1 is a flowchart of a method 100 for fabricating apackage-on-package according to various aspects of the presentdisclosure. Referring to FIG. 1 , the method includes block 110, inwhich a first package component is provided, the first package componenthaving a first die formed on a first substrate. The method 100 includesblock 120, in which a second package component is provided, the secondpackage component having a second die formed on a second substrate. Themethod 100 includes block 130, in which a thermal isolation material isattached to the first die. The thermal isolation material substantiallythermally insulates the second die from the first die. The method 100includes block 140, in which the first package component is coupled tothe second package component with a set of conductive elements.

It is understood that additional processes may be performed before,during, or after the blocks 110-140 shown in FIG. 1 to complete thefabrication of the package-on-package structure, but these additionalprocesses are not discussed herein in detail for the sake of simplicity.

FIGS. 2-6 are diagrammatic fragmentary cross-sectional side views of atop package and/or a bottom package at various fabrication stages ofmanufacturing a package-on-package structure according to embodiments ofthe method 100 of FIG. 1 . It is understood that FIGS. 2-6 have beensimplified for a better understanding of the inventive concepts of thepresent disclosure. It should be appreciated that the materials,geometries, dimensions, structures, and process parameters describedherein are exemplary only, and are not intended to be, and should not beconstrued to be, limiting to the invention claimed herein. Manyalternatives and modifications will be apparent to those skilled in theart, once informed by the present disclosure.

An embodiment package-on-package structure will be discussed withreference to FIGS. 2-6 . FIG. 2 illustrates a top package 1 to beemployed in the package-on-package structure. Top package 1, which maybe formed using a plastic ball grid array (PBGA) package assemblyprocess or the like, includes a plurality of stacked die 2, which may bewired bonded to top substrate 10 by way of contacts 16 (on respectivestacked die 2), bond wires 6, and contacts 12 (on top substrate 10).Individual stacked die may comprise a memory chip, a logic chip, aprocessor chip, or the like. Although FIG. 2 illustrates three stackeddie, this is for illustration only. Likewise, the use of wire bonding ismerely illustrative, and other approaches for electrically connectingthe stacked die are within the contemplated scope of the presentdisclosure. For example, solder bumps, solder balls, copper pillars,conductive bumps, solder caps, conductive pillars, conductive balls,under-bump metallurgies, and/or other connector elements may also becontemplated to connect stacked die 2 to top substrate 10. In someembodiments, an underfill (not shown) is dispensed into the gap betweenstacked die 2 and top substrate 10 to reinforce the strength of thepackage-on-package structure.

Top substrate 10 may be a laminated circuit board comprised ofalternating layers of non-conductive polymers, such asbismaleinide-triazine (BT), and patterned (or non-patterned) conductivelayers. As discussed above, top substrate 10 has contacts 12 on a firstside (referred to herein sometimes as a top side for convenience) forelectrical connection to stacked die 2. Top substrate 10 further hasbottom contacts 24 on a second side (sometimes referred to as a bottomside) for electrical connection to other components as will be detailedfurther below. Solder balls 36 are attached to bottom contacts 24 to topsubstrate 10. Solder balls 36 allow for electrical and/or thermalconnection between top package 1 and a bottom package 34 (not shown inFIG. 2 , but illustrated in FIGS. 3 and 4 ). In the illustratedembodiment, solder balls 36 provide for electrical conduction of signalsand power to stacked die 2. Again, other connection components, such asconductive bumps, conductive balls, conductive pillars, and the like,could be employed in lieu of solder balls 36.

In some embodiments, a molding compound 35 is applied to top package 1to provide mechanical stiffness and enhance the mechanical strength ofthe package-on-package structure. It is believed that this mechanicalstiffness prevents, or at least reduces, the severity of warpagesresulting from, for example, thermal expansion mismatch between thecomponents of the resulting package. Molding compound 35 may be moldedon substrate 10 and surrounds stacked die 2 and bond wires 6 using, forexample, compressive molding or transfer molding. A curing step may thenbe performed to solidify the molding compound 35. The molding compound35 may comprise a polymer-based material, an underfill, a moldingunderfill (MUF), an epoxy, or the like.

Top package 1 is attached to a bottom package 34, as illustrated in FIG.5 byway of solder balls 36. As depicted in FIG. 3 , the bottom package34 includes die 37, which is flip chip attached to a bottom substrate38, and which is electrically connected thereto by way of connectorelements 39. Die 37 may comprise a logic chip, a processor chip, amemory chip, or the like. Connector elements 39 may include, for examplesolder bumps, solder balls, copper pillars, conductive bumps, soldercaps, conductive pillars, conductive balls, and under-bump metallurgies.In some embodiments, an underfill (not shown) is dispensed into the gapbetween die 37 and bottom substrate 38 to reinforce the strength of thepackage-on-package structure. Electrical connection between die 37 andan underlying mother board or other circuitry (not shown) is provided bythrough vias (not shown) aligned with connector elements 39 on one sideof bottom substrate 38 and connector elements 42 on the other side ofbottom substrate 38. Likewise, electrical connection between topsubstrate 10 and an underlying mother board or other circuitry isprovided by solder balls 36, through vias, and connector elements 42.

In operation, both the bottom package 34 and the top package 1 thatinclude die 37 and stacked die 2, respectively generate heat. Heat thatis generated by die 37, especially where the bottom die is a processordie, may cause damage to the top die or stacked die 2. The heat can alsocause thermal stress and warpage in the package-on-package structureleading to cracks in the connector elements, such as solder balls. Anadvantageous feature of the package-on-package structure of the presentdisclosure is a thermal isolation material 50 of the bottom package 34,as depicted in FIG. 3 , attached above die 37 and thermally insulatesstacked die 2 from the heat generated by die 37. In one embodiment, asan additional benefit because the top package 1 and bottom package 34are insulated from heat thanks to the thermal isolation material 55,warpage in the package-on-package structure is better controlled. Inother words, thermal isolation material 55 provides resistance towarping that might otherwise occur as a result of thermal coefficient ofexpansion (CTE) mismatch between top package 1 and bottom packager 34.

In some embodiments, the thermal isolation material 50 is a materialhaving a thermal conductivity of from about 0.024 W/mK to about 0.2W/mK. The thermal isolation material 50 may comprise a porous film, awax film, a die attach film (DAF), an aerogel, a tape, a thermalinterface material (TIM), or an adhesive. Where the thermal isolationmaterial 50 is a TIM, the TIM may comprise a solder paste, an adhesive,or thermal grease. In some embodiments, the thermal isolation material50 has a thickness ranging from about 10 microns to about 100 microns.

FIG. 5 shows the thermal isolation material 50 in the package-on-packagestructure where the bottom package 34 is attached to the top package 1.

In other embodiments, the thermal isolation material 50 is a seal ring55 having air or vacuum 77 therein, as shown in FIG. 4 and as shown inFIG. 6 . The seal ring 55 is formed in the package-on-package structurewhere the bottom package 34 is attached to top package 1. Air or vacuumis an ideal thermal insulator under normal operation conditions. Inother embodiments, the seal ring 55 provides a thermal conductivity ofabout 0 W/mK. Seal ring 55 is dispensed on die 37 to provide a vacuumgap during a molding process that will be explained below.

After either the thermal isolation material 50 or the seal ring 55 hasbeen applied to die 37, in some embodiments, a molding compound 35 isapplied to bottom package 34 to provide mechanical stiffness and enhancethe mechanical strength of the package-on-package structure. Moldingcompound 35 may be molded on substrate 38 and surround die 37 andconnector elements 39 using, for example, compressive molding ortransfer molding. A curing step may then be performed to solidify themolding compound 35. The molding compound 35 may comprise apolymer-based material, an underfill, a molding underfill (MUF), anepoxy, or the like. Referring back to FIG. 4 , to form the air or vacuum77, the molding compound 35 is formed around the seal ring 55, therebyencapsulating the air or vacuum 77 therein.

The package-on-package structures shown in FIGS. 2-6 are only forillustrative purpose and are not limiting. Additional embodiments can beconceived.

Advantages of one or more embodiments of the present disclosure mayinclude one or more of the following.

In one or more embodiments, in a package-on-package structure having atop package with a top die and a bottom package with a bottom die, thetop die is substantially insulated from the heat generated by the bottomdie.

In one or more embodiments, warpage in a package-on-package structure isbetter to control because the top package and the bottom package aresubstantially insulated from heat.

The present disclosure has described various exemplary embodiments.According to one embodiment, a semiconductor device includes a firstpackage component and a second package component. The first packagecomponent has a first die formed on a first substrate. The secondpackage component has a second die formed on a second substrate. A firstset of conductive elements couples the first package component to thesecond package component. A thermal isolation material is applied on thefirst die and interjacent the first package component and the secondpackage component, wherein the thermal isolation material thermallyinsulates the second die from the first die. In some embodiments, thethermal isolation material includes a seal ring and an air gap.

According to another embodiment, a package-on-package includes a bottompackage component and a top package component. The bottom packagecomponent has at least a bottom die formed on a bottom substrate. Thetop package component has at least a top die formed on a top substrate.A thermal isolation material is attached to the bottom die, wherein thethermal isolation material thermally insulates the top die from thebottom die. The thermal isolation material has a thermal conductivity offrom about 0.024 W/mK to about 0.2 W/mK. A first set of conductiveelements couples the bottom substrate to the top substrate. In someembodiments, the thermal isolation material includes a seal ring and anair gap.

According to yet another embodiment, a method of forming a package isdisclosed. A first package component is provided, and the first packagecomponent has a first die formed on a first substrate. A second packagecomponent is provided, and the second package component has a second dieformed on a second substrate. A thermal isolation material is attachedto the first die, wherein the thermal isolation material thermallyinsulates the second die from the first die. The first package componentis coupled to the second package component with a first set ofconductive elements. In some embodiments, the thermal isolation materialincludes a seal ring and an air gap.

In the preceding detailed description, specific exemplary embodimentshave been described. It will, however, be apparent to a person ofordinary skill in the art that various modifications, structures,processes, and changes may be made thereto without departing from thebroader spirit and scope of the present disclosure. The specificationand drawings are, accordingly, to be regarded as illustrative and notrestrictive. It is understood that embodiments of the present disclosureare capable of using various other combinations and environments and arecapable of changes or modifications within the scope of the claims.

What is claimed is:
 1. A method comprising: disposing a thermalisolation material on a top surface of a die, wherein the die iscomprised in a lower package component, and wherein at a time thethermal isolation material is disposed, outer edges of the thermalisolation material are aligned to corresponding edges of the die;bonding an upper package component to the lower package component,wherein the thermal isolation material is between, and is in contactwith, both of the die and the upper package component; and after theupper package component is bonded to the lower package component,disposing a molding compound between the upper package component and thelower package component.
 2. The method of claim 1, wherein the thermalisolation material is a solid plate that continuously extends from afirst edge of the die to an opposing second edge of the die.
 3. Themethod of claim 1, wherein the thermal isolation material comprises aporous film.
 4. The method of claim 1, wherein the thermal isolationmaterial comprises an aerogel.
 5. The method of claim 1, wherein thethermal isolation material has a thermal conductivity value in a rangebetween about 0.024 W/mK and about 0.2 W/mK.
 6. The method of claim 1,wherein the molding compound is dispensed in a flowable form, and themethod further comprises curing to solidify the molding compound.
 7. Themethod of claim 1, wherein the thermal isolation material is in a formof a seal ring encircling a space therein, and wherein after the upperpackage component is bonded to the lower package component, an air gapor vacuum is enclosed by the seal ring, the upper package component, andthe die.
 8. The method of claim 7, wherein the molding compound is incontact with the outer edges of the seal ring, with the outer edges ofthe seal ring being the outer edges of the thermal isolation material,and wherein inner edges of the seal ring are exposed to air or vacuum.9. The method of claim 8, wherein the seal ring encircles air therein.10. The method of claim 7, wherein the seal ring encircles a vacuumedspace therein.
 11. A method comprising: forming a lower packagecomprising a device die; bonding an upper package over the lowerpackage; and forming a filling region between the lower package and theupper package, wherein the filling region encircles a space that isbetween the upper package and the device die, and the space comprises anair space or a vacuumed space.
 12. The method of claim 11, wherein thefilling region comprises: attaching a first material in a regiondirectly over the device die; and dispensing a second materialvertically offset from the device die, wherein the second material isdifferent from the first material.
 13. The method of claim 12, whereinthe first material and the second material have interfaces that arevertically aligned to outer edges of the device die.
 14. The method ofclaim 12, wherein the first material and the second material areattached to the device die through different processes.
 15. A methodcomprising: forming a lower package component comprising bonding a dieto a substrate; forming a seal ring on a first top surface of the die;bonding a upper package component to the lower package component,wherein a space is defined by the upper package component, the die, andthe seal ring; and dispensing an encapsulant between, and contactingboth of, the upper package component and the lower package component, sothat the space and the seal ring are encircled by the encapsulant,wherein the encapsulant and the seal ring form interfaces that extendfrom a bottom surface to a second top surface of the seal ring, and theinterfaces are vertically aligned to corresponding edges of the die. 16.The method of claim 15 further comprising curing the encapsulant. 17.The method of claim 15, wherein at a time after the encapsulant isdispensed, the space is an air gap.
 18. The method of claim 15, whereinat a time after the encapsulant is dispensed, the space is a vacuumedspace.
 19. The method of claim 15, wherein the seal ring comprises inneredges that face the space, and the inner edges are vertical and straightedges.
 20. The method of claim 15, wherein the encapsulant is dispensedafter the seal ring is formed.